Thyroid Lab Assessment

Question 1

Thyroid Function Tests

Answer 1

Thyroid-Stimulating Hormone (TSH)
Thyroxine (T4)—Total Serum level
Triiodothyronine (T3)—Total Serum level
 Free T4 Index—calculation of Free T4 (FTI)
T3 Resin Uptake (Used to calculate FTI)

Thyroglobulin Antibody (Tg-Ab)
Thyroid Peroxidase Antibody (TPO-Ab)
Thyroid stimulating hormone receptor antibody (Anti-TSHR)

Question 2

The best assessment of thyroid function

Answer 2

TSH

Question 3

Elevated TSH is seen in the following conditions

Answer 3

Hypothyroidism  
Thyroiditis
Thyroid agenesis (newborn's; screened by law)
Pituitary tumor
Other severe and chronic illnesses
Drug effects: Iodine, Thyroxine

Question 4

Low TSH in these conditions

Answer 4

Hyperthyroidism
Damage to the pituitary gland that prevents it from making TSH (Secondary hypothyroidism)
Hypothalamus insufficiency (Tertiary hyperthyroidism)
Taking too much thyroid medicine for treatment of an underactive thyroid gland
Drugs: excess T4 therapy, glucocorticoids, L-dopa

Question 5

Thyroxine (T4)

Answer 5

Prominent thyroid hormone (>90%)
Nearly all of it is transported bound to proteins:
Thyroxine binding globulin (TBG)
Albumin
Transthyretin (thyroxine-binding prealbumin–TBPA)
Only free (unbound) is metabolically active
Total measures bound and free hormone

Question 6

Total T4 Levels Increased

Answer 6

Hypothyroid states
Pituitary insufficiency
Hypothalamic failure
Protein malnutrition/depletion  (WHY?)
Iodine insufficiency
Numerous other non-thyroid illnesses (CRF, Cushings, cirrhosis, advanced cancer)

Question 7

Total T4 Levels Decreased

Answer 7

Hyperthyroidism
Acute thyroiditis
Conditions causing increased TBG 
Pregnancy
Meds listed on previous slide

Question 8

Results of T3 Resin Uptake: Hyperthyroidism

Answer 8

High T4, high T3 resin uptake or THBI, high free index T4

Question 9

Results of T3 Resin Uptake: Hypothyroidism

Answer 9

Low T4, low T3 resin uptake or THBI, low free index T4

Question 10

Results of T3 Resin Uptake TBG excess

Answer 10

High T4, low T3 resin uptake or THBI, normal free index T4

Question 11

Results of T3 Resin Uptake TBG defiency

Answer 11

Low T4, high T3 resin uptake or THBI, normal free index T4

Question 12

Anti Tg and Anti TPO

Answer 12

looking for autoimmune diseases such as Hashimotos and Grave’s disease

Question 13

TSH-stimulating Ab/TSH-blocking Ab

Answer 13

Grave’s disease and Hashimoto’s

Question 14

TSH, Free T4

Answer 14

initial labs to establish hypothyroidism or hyperthyroidism, also used to monitor therapy

Question 15

TBG

Answer 15

measures amount of binding proteins

Question 16

FTI

Answer 16

can help determine if true elevation or depression or T4 or T3

Question 17

measure TSH

Answer 17

If it is low usually indicates probable overt hyperthyroidism
If it is high more suspicious for cancer

Question 18

Interpreting a radionuclide Thyroid scan: HOT nodule

Answer 18

rapid uptake of iodine or isotope

Less likely to be malignant

Question 19

Interpreting a radionuclide Thyroid scan: COLD nodule

Answer 19

little or no uptake of iodine or isotope

More likely to be malignant